New submission from Wolfgang Maier <wolfgang.ma...@biologie.uni-freiburg.de>:
from https://docs.python.org/3/library/random.html#random.choice: Return a random element from the non-empty sequence seq. If seq is empty, raises IndexError. Indeed: >>> import random >>> random.choice([]) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/wolma/cpython/random.py", line 259, in choice raise IndexError('Cannot choose from an empty sequence') from None IndexError: Cannot choose from an empty sequence but when not using getrandbits internally: >>> class MyRandom(random.Random): ... def random(self): ... return super().random() ... >>> my_random=MyRandom() >>> my_random.choice([]) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/wolma/cpython/random.py", line 257, in choice i = self._randbelow(len(seq)) File "/home/wolma/cpython/random.py", line 245, in _randbelow rem = maxsize % n ZeroDivisionError: integer division or modulo by zero This is because the ValueError that random.choice tries to catch gets raised only in the getrandbits-dependent branch of Random._randbelow, but not in the branch using only Random.random (even though Random._randbelow suggests uniform behaviour. ---------- components: Library (Lib) messages: 314787 nosy: rhettinger, serhiy.storchaka, wolma priority: normal severity: normal status: open title: random.choice: raise IndexError on empty sequence even when not using getrandbits internally type: behavior versions: Python 3.6, Python 3.7, Python 3.8 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue33203> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
